1. Field of the Invention
The invention concerns a process of producing an article of thermosetting resin and a flexible, compressible thermosetting resin impregnated open-cell sheet useful in the process.
2. Description of the Prior Art
British Patent Application No. 1,266,097 describes a process for making an article of thermosetting resin which comprises (a) impregnating a sheet having an open-cell structure with a curable thermosetting resin, (b) applying a layer of fibrous reinforcing material to at least one side of the impregnated foam sheet, (c) compressing the foam sheet and reinforcing layer to the extent that resin is expelled from the sheet into the fibrous reinforcing layer so as to impregnate this layer with resin throughout its thickness, and (d) allowing the resin in the sheet and layer to cure while maintaining the compression. The process described in the British patent is an entirely new way to make laminated-type articles.
It is generally known in the art that gas release agents (also referred to as blowing agents or foaming agents) have been used for years to mix with curable thermosetting resins to form foamable compositions which generally form light weight thermoset foams. See for example U.S. 3,320,187 to Burt; U.S. 3,373,121 to Burgert and Moore; U.S. 3,282,863 to Carey and Jones; and U.S. 3,252,923 to Salgado and Berlinger.
Surprisingly, it has now been discovered that by using a curable thermosetting resin in which there is incorporated a small amount of a gas release agent as the curable thermosetting resin in the process described in British Patent 1,266,097 the expulsion of the resin from the foam sheet into the fibrous reinforcing layer is promoted and as a result less resin is required in the process.
In the process disclosed in British Patent No. 1,266,097 it is necessary that sufficient resin is expelled from the foam sheet to thoroughly impregnate the adjacent fibrous reinforcing layer. The resin is driven into the fibrous layer by compression of the foam sheet, and usually, although generally low pressures are needed, a rather high compression of the foam sheet is required to achieve adequate impregnation of the fibrous layer. Accordingly, the extent of compression of the foam sheet is dictated by this impregnation requirement, and there is no complete freedom to apply the compression on the basis of desired final thickness of the product or the final density or porosity of the compressed foam sheet.
An object of this invention is to make the earlier proposed method more widely applicable. Accordingly, the present invention is an improvement in the process referred to above, wherein gas pressure is generated in the cells of the impregnated foam sheet to promote the expulsion of resin from the first sheet into the reinforcing layer.